1. Field of the Invention
The present invention relates to an improvement in an optical apparatus and camera with a line of sight detection function.
2. Related Background Art
Conventionally, a single-lens reflex camera detects the line of sight direction (watched point) of an observer to recognize the position on the frame the user is observing, and uses that information in, e.g., focus detecting area selection, or the like of an automatic focus detecting device.
A line of sight detection scheme suitable for a camera obtains a line of sight using the positional relationship between the pupil and a cornea reflected image (Purkinje image) based on light projected from a light source onto the front eye portion of the person under examination, and reflected by the cornea, as disclosed in, e.g., Japanese Patent Application Laid-Open No. 6-294930.
Also, Japanese Patent Application Laid-Open No. 2-32312 discloses the method of using watched point information suitable for focus detecting area selection. In this method, a line of sight position detected based on a signal generated in response to first-stroke operation (switch SW1=ON) of a release button is fixed, automatic focus adjustment is done at that position, and a shutter release circuit operates based on a signal generated in response to second-stroke operation (switch SW2=ON) of the release button. In this manner, the user need not select a specific one of a plurality of focus detecting areas. Around 100 focus detecting areas of the single-lens reflex camera can be set using an area type focus detecting technique proposed in Japanese Patent Application Laid-Open No. 9-184965 by the present applicant, and distance measuring point selection gains a its importance as the number of focus detecting areas increases.
However, selection of a focus detecting area based on the detection result of the watched point does not always result in quick photographing which is preferable in terms of composition, for the following reasons.
First, it is difficult to match the position to be focused on an object, watched point, and focus detecting area with each other. When a large number of focus detecting areas are placed at high density, since focusing is allowed at a desired position within the photographing frame, such areas are very advantageous for composition-priority photographing. However, if the positions of the focus detecting areas are displayed within the viewfinder, they may disturb object viewing since they are dense.
In one method devised to avoid such situation, the focus detecting areas are not displayed upon depression of the release button, and after a given focus detecting area is selected based on watched point information, that focus detecting area is displayed to assure a sufficient field of view for object observation. This method assumes the position to be focused on the object matches the watched point; it selects a focus detecting area close to that position later. However, since a display pattern that indicates the focus detecting areas is not displayed initially, a focus detecting area is not always present on the watched point, and whether or not the watched point is located on a focus detecting area is purely a stochastic question. If a rule for selecting a closest focus detecting area when no focus detecting area is present on the watched point is adopted, the user's will is not reflected unless focus detecting areas are placed at higher density.
As another method of avoiding the aforementioned drawback, a technique disclosed in Japanese Patent Application Laid-Open No. 9-160111 is extended; a watched point indication whose color, shape, or the like is different from that on a focus detecting area is displayed in areas other than the focus detecting areas within the viewfinder. In this case, focus adjustment is done after the user directs the camera toward the object and confirms that an indication that indicates if the watched point is located on a focus detecting area is ON. More specifically, priority is given to matching between the watched point and focus detecting area.
However, since the gap between neighboring focus detecting areas is in question now, the watched point does not match a focus detecting area, and non-coincidence between the watched point and focus detecting area may be detected initially. In such case, the user appropriately moves the line of sight to seek a position where the watched point matches a focus detecting area and the indication pattern changes. However, since the user has moved the line of sight, the watched point does not match the position to be focused on the object in turn. Hence, the user fixes the line of sight with respect to the camera, and adjusts the watched point and focus detecting area by turning together with the camera. In this case, a camera which can quickly adjust the focus to the watched point cannot be realized.
Second, selection of a focus detecting area based on the detection result of the watched point does not always result in quick photographing which is preferable in terms of composition, because of uncertainty of the watched point.
In general, motions of the eyeballs of a human being include a saccadic eye movement which takes place upon extracting image features and has a maximum rate of eyeball rotation angle as high as 300.degree./sec, a pursuit eye movement which takes place for a moving object at 30 to 35.degree./sec or less and is a slow and smooth movement, an involuntary eye movement which takes place involuntarily to capture a target object at the center and is an irregular, infinitesimal motion, and the like.
Since the eye of the user catches the target object upon pressing the release button, the pursuit and involuntary eye movements of these motions have taken place. Even in the involuntary eye movement of the eyeball, the user consciously watches one point on the target object. It is commonly held in physiological optics that the eye does not always catch one point on the target object in terms of an eyeball motion, but catches one point in terms of perception.
More specifically, this also means that the watched point as an eyeball motion detected at the first-stroke position of the release button may not always be the one the user consciously watched at that instance. Hence, the watched point detected as an eyeball motion is uncertain to some extent.
As described above, in the conventional line of sight input type auto-focus camera, upon matching (1) the position to be focused on the object, (2) the watched point, and (3) the focus detecting area, if (1) and (2) are determined beforehand on the condition that (2) the watched point is commonly used, a problem is posed upon determining (3); if (2) and (3) are determined beforehand, a problem occurs upon determining (1), thus disturbing quick focus adjustment. In this manner, two problems are posed, i.e., the three factors do not match each other, and the detection result of the watched point used therefor does not perfectly correspond to the user's watching consciousness.
These problems are especially serious upon photographing a moving object. More specifically, when the focus detecting area selected based on the line of sight is not located on the object and the focus is adjusted to the background, or when an unexpected focus detecting area is selected based on the watched point information, the object position is changing constantly even if the user wants to redo focusing. As a result, an image which is preferable in terms of composition can no longer be obtained, and it is impossible to redo focusing in practice. In association with the focus adjustment mode of the camera, the user often misses an important photographing chance due to selection of a focus detecting area based on the input line of sight in a servo AF mode that continuously adjusts the focus to a moving object.